Auto Power-On¶

The Auto Power-On feature allows the LattePanda Sigma 2 to start up automatically when power is supplied, without pressing the physical power button — essential for embedded and unattended deployments.

LattePanda Sigma 2 offers two ways to achieve this:

DIP Switch — hardware-level, no BIOS setting required.
Onboard MCU (RP2350) — programmable, offering enhanced flexibility, e.g. powering on under custom conditions.

Configure via DIP Switch¶

Locate the onboard DIP switch.
Set the APO actuator:

Actuator Position Behavior

OFF (Default) Requires pressing the power button to turn on after power is applied.

ON Automatically powers on when power is applied.

Note

Only this actuator of the DIP switch needs to be set; no modifications are required in the BIOS settings!
This setting takes effect immediately, and is unaffected by the RTC battery.

Configure via Onboard MCU¶

The RP2350 co-processor's GPIO18, GPIO19 and GPIO20 are internally connected to the board's S0 state pin, S3 state pin and SW (power button) pin respectively. The RP2350 can therefore read the system's power state and "press" the power button by itself — enabling auto power-on under custom conditions.

RP2350 Pin	Board Connection
GPIO18	Internally Connected to `S0` State Pin
GPIO19	Internally Connected to `S3` State Pin
GPIO20	Internally Connected to `SW` Button
GPIO21	Internally Connected to `RST` Button
GPIO22	Internally Connected to `S4` State Pin

The state pins in different system states behave as follows:

	Powered but not turned on	Run	Sleep/Suspend (Modern Standby)	Hibernate	Shut Down
S0 Pin	Low	High	Low	Low	Low
S3 Pin	Low	Low	High	Low	Low
S4 Pin	Low	Low	Low	High	Low

For details, please refer to the RP2350 GPIO Mapping and GPIO Header sections.

The following will demonstrate how to use the MCU to achieve auto power-on when external power is supplied.

Keep the RP2350 Powered

Set the MCU actuator of the DIP switch to ON, so that the RP2350 is supplied with power whenever the board receives power input — even before the system is turned on. Please refer to the DIP Switch section.

Note

The DIP switch controls the MCU's power supply only before the system is turned on; in other states it is configured by the MCU Power Control setting in the BIOS (default Auto: powered while running and sleeping) — please refer to the MCU Power Control section.

Upload the Auto Power-On Code

The RP2350 ships with MicroPython firmware pre-loaded. Using Thonny, save the following code as main.py on the RP2350 — please refer to the MicroPython section for detailed steps:

from machine import Pin
import time

S0 = Pin(18, Pin.IN)
S3 = Pin(19, Pin.IN)
SW = Pin(20, Pin.IN)   # High-impedance input = button released

time.sleep(1)          # Wait for the power supply to stabilize

# The check below runs only once, when the RP2350 starts up.
# If the system is off (power was just reconnected), press the power button.
while S0.value() == 0 and S3.value() == 0:  # System is off
    SW.init(Pin.OUT)
    SW.value(0)                          # Press the power button
    time.sleep_ms(500)
    SW.init(Pin.IN)                      # Release the button
    time.sleep(1)                        # Wait and re-check the state

# main.py ends here and the RP2350 stays idle, so a later manual
# shutdown stays off until the next power cycle.

If you prefer Arduino C++, upload the following sketch instead — please refer to the Arduino C++ section:

/*
 * LattePanda Sigma 2 Auto Power-On via onboard RP2350
 */
#define PIN_S0 18  // System status pin
#define PIN_S3 19  // System status pin
#define PIN_SW 20  // Power button pin

void setup() {
  pinMode(PIN_S0, INPUT);
  pinMode(PIN_S3, INPUT);
  pinMode(PIN_SW, INPUT);  // High-impedance = button released
  delay(1000);             // Wait for the power supply to stabilize

  // The check below runs only once, when the RP2350 starts up.
  // If the system is off (power was just reconnected), press the power button.
  while (digitalRead(PIN_S0) == LOW && digitalRead(PIN_S3) == LOW) {  // System is off
    pinMode(PIN_SW, OUTPUT);
    digitalWrite(PIN_SW, LOW);   // Press the power button
    delay(500);
    pinMode(PIN_SW, INPUT);      // Release the button
    delay(1000);                 // Wait and re-check the state
  }
}

void loop() {
  // Intentionally empty: a later manual shutdown stays off
  // until the next power cycle.
}

Both programs work the same way: the check runs only once, when the RP2350 starts up. If the system is off at that moment (both S0 and S3 are LOW, i.e. the power supply was just reconnected), the RP2350 pulls the SW pin LOW for 500 ms — equivalent to pressing the power button — then releases it. Afterwards the programs stay idle.

Verify Auto Power-On Function

Shut down the LattePanda, disconnect the power supply, then reconnect it. The LattePanda should power on automatically within a few seconds.

Note

This method is unaffected by the RTC battery.

Join our Discord

Actuator Position	Behavior
OFF (Default)	Requires pressing the power button to turn on after power is applied.
ON	Automatically powers on when power is applied.